overview of 3d object representations - princeton ... overview of 3d object representations thomas...

17
1 Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations What makes a good 3D object representation? Stanford and Hearn & Baker

Upload: vanlien

Post on 11-Mar-2018

229 views

Category:

Documents


3 download

TRANSCRIPT

Page 1: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

1

Overview of3D Object Representations

Thomas Funkhouser

Princeton University

C0S 597D, Fall 2003

3D Object Representations

• What makes a good 3D object representation?

Stanford andHearn & Baker

Page 2: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

2

3D Object Representations

• What makes a good 3D object representation?� Intuitive specification� Guaranteed continuity� Guaranteed validity� Efficient rendering� Efficient boolean operations� Accurate� Concise� Structure

3D Reps for Computer Graphics

• Raw data� Point cloud� Range image� Voxels� Polygon soup

• Surfaces� Mesh� Subdivision � Parametric� Implicit

• Solids� Octree� BSP tree� CSG

• High-level structures� Scene graph

Page 3: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

3

Point Cloud

• Unstructured set of 3D point samples� Acquired from range finder, computer vision, etc

Hoppe

Hoppe

Range Image

• Set of 3D points mapping to pixels of depth image� Acquired from range scanner

Brian CurlessSIGGRAPH 99 Course #4 Notes

Range Image Tesselation Range Surface

Page 4: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

4

Voxels

• Uniform grid of volumetric samples� Acquired from CAT, MRI, etc.

FvDFH Figure 12.20

Stanford Graphics Laboratory

Polygon Soup

• Unstructured set of polygons� Created with interactive modeling systems?

Larson

Page 5: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

5

3D Reps for Computer Graphics

• Raw data� Point cloud� Range image� Voxels� Polygon soup

• Surfaces� Mesh� Subdivision � Parametric� Implicit

• Solids� Octree� BSP tree� CSG

• High-level structures� Scene graph

Mesh

• Connected set of polygons (usually triangles)� Efficient rendering

Stanford Graphics Laboratory

Page 6: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

6

Subdivision Surface

• Define surfaces as limit of refinement sequence� Guaranteed continuity, concise

Zorin & SchroederSIGGRAPH 99

Course Notes

Parametric Surface

• Tensor product spline patchs� Intuitive specification?, guaranteed continuity?,

accurate?, concise

FvDFH Figure 11.44

Page 7: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

7

Implicit Surface

• Points satisfying: F(x,y,z) = 0� Guaranteed continuity, guaranteed validity, efficient

boolean operations, concise?

Polygonal Model Implicit ModelBill Lorensen

SIGGRAPH 99Course #4 Notes

3D Reps for Computer Graphics

• Raw data� Point cloud� Range image� Voxels� Polygon soup

• Surfaces� Mesh� Subdivision � Parametric� Implicit

• Solids� Octree� BSP tree� CSG

• High-level structures� Scene graph

Page 8: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

8

Octree

• Binary space partition with solid cells labeled� Guaranteed validity, efficient boolean operations

FvDFH Figure 12.25

BSP Tree

• Binary space partition with solid cells labeled� Guaranteed validity, efficient boolean operations

a

b

c

d

e

f

1

2

3

7

4

5

6

a

bc

de

fg

Object

a

b

cdef

1

2

3

4

5

6

7

Binary Spatial Partition

Binary Tree

Naylor

Page 9: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

9

CSG

• Hierarchy of boolean set operations (union, difference, intersect) applied to simple shapes� Intuitive specification, guaranteed validity,

efficient boolean operations

FvDFH Figure 12.27 H&B Figure 9.9

3D Reps for Computer Graphics

• Raw data� Point cloud� Range image� Voxels� Polygon soup

• Surfaces� Mesh� Subdivision � Parametric� Implicit

• Solids� Octree� BSP tree� CSG

• High-level structures� Scene graph

Page 10: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

10

Scene Graph

• Union of objects at leaf nodes� Efficient rendering, high-level structure

Bell Laboratories

avalon.viewpoint.com

3D Reps for Computer Graphics

• Raw data� Point cloud� Range image� Voxels� Polygon soup

• Surfaces� Mesh� Subdivision � Parametric� Implicit

• Solids� Octree� BSP tree� CSG

• High-level structures� Scene graph

Page 11: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

11

Equivalence of Representations

• Thesis:� Each fundamental representation has enough

expressive power to model the shape of any geometric object

� It is possible to perform all geometric operations with any fundamental representation!

• Analogous to Turing-Equivalence:� All computers today are turing-equivalent,

but we still have many different processors

Computational Differences

• Efficiency� Combinatorial complexity (e.g. O( n log n ) )� Space/time trade-offs (e.g. z-buffer)� Numerical accuracy/stability (degree of polynomial)

• Simplicity� Ease of acquisition� Hardware acceleration� Software creation and maintenance

• Usability� Designer interface vs. computational engine

Page 12: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

12

3D Reps for Computer Graphics

• Different properties for different applications

Intuitive specification Yes NoGuaranteed continuity Yes NoGuaranteed validity Yes NoEfficient boolean operations Yes NoEfficient rendering Yes YesAccurate Yes YesConcise ? ?Structure Yes Yes

Edi

ting

Dis

play

Property

3D Reps for Analysis & Retrieval

• Different properties for different applications

Intuitive specification Yes No No NoGuaranteed continuity Yes No No NoGuaranteed validity Yes No No NoEfficient boolean operations Yes No No NoEfficient rendering Yes Yes No NoAccurate Yes Yes ? ?Concise ? ? ? YesStructure Yes Yes Yes Yes

Edi

ting

Dis

play

Ana

lysi

s

Ret

riev

al

Property

Page 13: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

13

3D Reps for Analysis & Retrieval • Statistical examples

� Moments� Wavelets� Extended Gaussian Image

• Structural examples� Medial axis� Curve skeletons� Deformable models

Moments

• Define shape by moments of inertia:

• Properties� Invertible� First-order moments give center of mass� Second-order moments give principal axes of rotation

�=surface

rqppqr dxdydzzyxm

Page 14: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

14

Wavelets

• Define shape with wavelet coefficients

• Properties� Invertible� Multiresolution

Jacobs, Finkelstein, & Salesin 1995

16,000 coefficients 400 coefficients 100 coefficients 20 coefficients

Extended Gaussian Image

• Define shape with histogram of normal directions� Invertible for convex objects� Spherical function

Page 15: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

15

3D Reps for Analysis & Retrieval

• Statistical examples� Moments � Wavelets� Extended Gaussian Image

• Structural examples� Medial axis� Curve skeletons� Deformable models

Medial Axis

• Define shape as union of centers of maximal balls

Nina Amenta

Page 16: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

16

Curve Skeleton

• Graph representing axis of local symmetry

Stanford Graphics Laboratory

Deformable Models

• Represent model as union of “part” primitives

Robert Osada

Page 17: Overview of 3D Object Representations - Princeton ... Overview of 3D Object Representations Thomas Funkhouser Princeton University C0S 597D, Fall 2003 3D Object Representations •

17

Summary

• Many possible 3D object representations� Most are “turing equivalent”� Different reps are more efficient for different tasks

• Shape analysis & retrieval� Not same requirements as modeling and rendering� We will study several different reps in this course